The present invention relates to a data storage system, and more specifically, this invention relates to efficient access to and management of data and resources in a tiered data storage system.
Tape-based data storage systems may include one or more tiers for storing data to tape media, and are typically used for storing and accessing large amounts of infrequently accessed data. This type of system may include a very large number of tape storage media (tape cartridges) for storing data, many tape drives to mount the tape cartridges when access to data on a particular tape cartridge is desired, and many servers (nodes), each server being connected to a limited number of the tape drives, for data access, i.e., for writing data to or reading data from the tape cartridges.
The tape drives and the tape cartridges are contained within tape libraries and each node that is connected to a tape drive of a tape library is able to access any tape cartridges contained within that tape library. However, because the number of tape drives in a tape library is typically much less than the number of tape cartridges, access to data stored to tape may require unwinding and unmounting a tape cartridge already in a tape drive in order to mount a different tape cartridge that has the data of interest stored thereon. Then, the tape cartridge is positioned to the data of interest.
Unmounting and mounting tape cartridges takes a long time when compared to storing data to or accessing data from an already-mounted tape cartridge. When mounting and/or unmounting is performed too often, it significantly decreases utilization of the tape drives for reading and writing, and consequently decreases the overall system throughput and request servicing capacity. This increases the average data access waiting time. Repositioning within the tape cartridge may also take a long time when not jointly optimized for multiple requests. These delays add up and decrease the overall efficiency of the data storage system.